Seems like your trying a different style of lyrics. I could hear this with dance music.

What music do you hear with it?

Suggestion:
With simplified lines, you want to make each carry its weight

Here lines 2 and 3 say the same thing.....use line 2 to add something....and since the lyrics are light on concrete details, try to fit some in on the new line.
....also vigilant might be difficult to sing as a rhyme with "silent"

I stay in the shadow
I don’t make a sound
Always silent......maybe "deathly/deadly silent" as foreshadowing
And always vigilant